As illustrated in FIG. 8, a steering apparatus is constructed so that movement of a steering wheel 1 is transmitted to a steering gear by way of a steering shaft 2, and a steering angle is applied to steered wheels 3 on the left and right. Moreover, the positional relationship between the steering wheel 1 and the driver changes depending on the size and driving posture of the driver, so tilt and telescopic steering apparatuses that have a function for adjusting the forward-backward position and up-down position of the steering wheel 1 are widely used.
FIG. 9 and FIG. 10 illustrate a conventional tilt and telescopic steering apparatus as disclosed in JP 2011-218941 (A). This steering apparatus has an electric powered power-steering apparatus that has: a steering shaft 2 that has a rear end to which a steering wheel 1 is fastened; a steering column 4 that supports the steering shaft 2 on the inside thereof so as to rotate freely; a steering-assist apparatus 5 that applies an assist torque to the steering shaft 2; and a steering gear unit 7 for causing tie rods 6 to displace based on the rotation of the steering shaft 2. In this specification, the forward-backward direction is the forward and backward direction of the vehicle.
The steering shaft 2 has an inner shaft 8 and outer shaft 9 that are combined together so as to be capable of transmitting rotation force, and capable of relative displacement in the axial direction. By the displacement in the axial direction of the inner shaft 8 and outer shaft 9, it becomes possible to not only adjust the forward-backward position of the steering wheel 1, but by the entire length of the steering shaft 2 contracting during a collision accident, it becomes possible to lessen impact on the driver that collides with the steering wheel 1.
The steering column 4 is formed by fitting the portion on the front-end side of an outer column 11 that is arranged on the rear side around the outside of the portion on the rear-end side of an inner column 10 that is arranged on the front side so that relative displacement is possible in the axial direction, and so as to be capable of extending or contracting in the axial direction with the steering shaft 2. The front-end section of the inner column 10 is connected and fastened to the rear-end surface of a gear housing 12 of the steering-assist apparatus 5. Moreover, the inner shaft 8 is inserted inside the gear housing 12, and the front-end section of the inner shaft 8 is connected to the input shaft of the steering-assist apparatus 5. The output shaft 13 of the steering-assist apparatus 5 is linked to the input shaft by way of a torsion bar, and the front-end section of the output shaft 13 protrudes from the front-end surface of the gear housing 12 and is linked to the steering-gear unit 7 by way of an intermediate shaft and universal joint.
The inner column 10 is supported by part of the vehicle body 15 by way of the gear housing 12 and a front-side support bracket 14. The gear housing 12 is supported by the front-side support bracket 14 so as to be able to pivot freely around a pivot shaft 16. The portion near the front end of the outer column 11 is supported by part of the vehicle body 15 by way of a rear-side support bracket 17. The rear-side support bracket 17 is supported by the vehicle body 15 so as to be able to separate in the forward direction when a strong impact is applied in the forward direction.
As illustrated in FIG. 10, in order to make it possible for the rear-side support bracket 17 to separate in the forward direction, connecting plates 19 are provided on the top-end sections of both of a pair of left and right support-plate sections 18 of the rear-side support bracket 17 so as to protrude out in a direction toward the sides of the steering column 4. Notches 20 are provided in the connecting plates 19 and are open on the rear-end edges of the connecting plates 19. Capsules 21 that are fastened to the vehicle body by bolts (not illustrated in the figure) are locked into the notches 20. Engaging grooves 22 for engaging with the edges on the left and right of the notches 20 of the connecting plates 19 are formed on the surfaces of the left and right sides of the capsules, and through holes 23 in the up-down direction through which the bolts are inserted are formed in the middle sections of the capsules 21.
During a collision accident, the driver's body applies a large impact load in the forward direction to the steering column 4 by way of the steering wheel 1 and steering shaft 2. As a result, the steering shaft 2 and steering column 4 have a tendency to contract over the entire length while absorbing the impact energy. When this happens, the rear-side support bracket 17 has a tendency to displace in the forward direction together with the outer column 11, however, both of the capsules 21 stay in their original positions together with the bolts. As a result, the capsules 21 come out toward the rear from the notches 20, which allows the steering wheel 1 to displace in the forward direction. A shock-absorbing mechanism that is constructed in this way absorbs the impact energy that is applied to the steering wheel 1 from the driver, and protects the driver.
Moreover, in order to make it possible to adjust the forward-backward position and the up-down position of the steering wheel 1, the outer column 11 is supported by the rear-side support bracket 17 so as to be able to displace in the forward-backward direction and in the up-down direction. More specifically, a column-side bracket 25 that has a pair of held sections 24 that are separated from each other in the width direction are integrally provided on the bottom surface of the front-end section of the outer column 11. Column-side through holes 26 that extend in the forward-backward direction are formed in the held sections 24 at positions that are aligned with each other. Moreover, vehicle-side through holes 27 that extend in the up-down direction are formed in portions of the support-plate sections 18 of the rear-side support bracket 17 that are aligned with each other and that are aligned with part in the forward-backward direction of the column side through holes 26. When the held sections 24 are held by the support-plate sections 18 of the support bracket 17, a rod-shaped member 28 is inserted through the column-side through holes 26 and vehicle-side through holes 27 from one end to the other (from the right side to the left side in FIG. 10), and a connecting nut 29 is screwed on the other end of the rod-shaped member 28. The connecting nut 29 can be freely turned by an adjustment lever 30.
The connecting nut 29 is rotated by the operation of the adjustment lever 30, and by expanding or contracting the space between the connecting nut 29 and the head section of the rod-shaped member 28, it is possible to expand or contact the space between the support-plate sections 18, which fastens or unfastens the outer column 11 to or from the rear-side support bracket 17; and it is possible to expand or contract the space between the held sections 24, which fastens or unfastens the outer column 11 to or from the inner column 10. With this kind of construction, when the space between the connecting nut 29 and the head section 31 is in the expanded state, it is possible to adjust the forward-backward position of the steering wheel 1 by causing the outer column 11 to displace in the forward-backward direction relative to the inner column 10 within the range (telescopic adjustment range) that the rod-shaped member 28 is able to displace inside the column-side through holes 26. Moreover, it is possible to adjust the up-down position of the steering wheel 1 by causing the steering column 4 to pivotally displace around the pivot shaft 16 within the range (tilt adjustment range) that the rod-shaped member 28 is able to displace inside the vehicle-side through holes 27.
On the other hand, FIG. 11 illustrates a conventional tilt steering apparatus that is disclosed in JP 2006-159920 (A) and has a bias spring 32 that applies a pressure force in the upward direction to the steering column 4a. The bias spring 32 is a so-called double-torsion spring that is formed, for example, by bending single wire that is made of spring steel, and is assembled so that a pair of coil-spring sections 33 that are provided on the portions near both ends of the wire are arranged so as to be in front of the rear-side bracket 17a, and by turning the pair of coil-spring sections 33, a tensile force is generated by these coil-spring sections 33 in the direction turned, and in that state, both end sections of the bias spring 32 engage with part of a front-plate section 34 that is provided on the front end of the rear-side support bracket 17a, and a pressure section 35 that is formed by the middle section of the wire causes a pressure force to act in the upward direction on the steering column 4a. 
By providing the bias spring 32, when the adjustment lever 30 is operated, the steering column 4a is prevented from pivoting downward due to gravity, and it is also possible to reduce the force needed when adjusting the height position of the steering column 4a. However, when the bias spring 32 is applied as a support mechanism for a steering column 4 in a tilt and telescopic steering apparatus that has the shock-absorbing mechanism illustrated in FIG. 9 and FIG. 10, there is a possibility that during a secondary collision, the bias spring 32 will also displace in the forward direction together with the outer column 11 and rear-side support bracket 17 to which both end sections of the bias spring 32 are fastened, and that the coil-spring sections 33 will collide against a member such as the gear housing 12 of a steering-assist apparatus 5 that is located further toward the front than the bias spring 32, and the bias spring 32 will be prevented from further displacement in the forward direction.
When the rear-side support bracket 17 and outer column 11 try to displace further in the forward direction with the bias spring 32 prevented from further displacement in the forward direction, there is a possibility that unless the fastened state of the bias spring 32 to the rear-side support bracket 17a is released, the bias spring 32 will be stuck between the rear-end section of the gear housing 12 and the rear-side support bracket 17, and will obstruct smooth displacement in the forward direction of the rear-side support bracket 17 and the outer column 11.
Moreover, even when the fastened state of the bias spring 32 to the rear-side support bracket 17 is released during a secondary collision, there is a possibility that as the rear-side support bracket 17 displaces further in the forward direction, the rear-side support bracket 17 and the coil-spring sections 33 will interfere with each other in the forward-backward direction, and will obstruct displacement of the rear-side support bracket 17a in the forward direction, and prevent smooth displacement in the forward direction of the rear-side support bracket 17 and outer column 11. A similar situation also occurs when a shock-absorbing mechanism that allows displacement in the forward direction of the steering column 4a and rear-side support bracket 17 during a secondary collision is applied to the tilt steering apparatus illustrated in FIG. 11.